Lens blocking device

ABSTRACT

A lens blocking device is described in which a pair of wedgeshaped prism rings may be adjusted relative to each other and relative to the base of the device for incorporating into the lens block a predetermined amount of prism at a predetermined meridianal orientation. Graduations measured in diopters are marked on the prism rings. Graduations measured in degrees are marked on the base. The lens blocking device contains means for supporting a lens blank to be blocked and for aligning the cylindrical and optical axes of a premarked lens blank with the device. Means are described for introducing a low melting point blocking metal into a mold cavity defined by the prism rings, the base and the lens blank. Means for cooling the blocking metal and for the easy removal of the solidifed block with attached lens blank are also described. Means are described for holding the prism rings in coaxial and rotatable contact with each other and with the base.

[ Feb. 18, 1975 LENS BLOCKING DEVICE [75] Lloyd F. Knight, BelleairBeach,

Fla.

Inventor:

Assignee: Textron, Inc., Tampa, Fla.

Filed: Dec. 10, 1973 Appl. No.: 423,448

References Cited UNITED STATES PATENTS 9/1966 Craddock 425/808 PrimaryExaminer-Francis S. Husar Assistant ExaminerV. K. Rising Attorney,Agent, or Firm-Ronald F. Ball; Charles B. Smith; Gary A. Walpert [57]ABSTRACT A lens blocking device is described in which a pair of vwedge-shaped prism rings may be adjusted relative to each other andrelative to the base of the device for incorporating into the lens blocka predetermined amount of prism at a predetermined meridianal orientation. Graduations measured in diopters are marked on the prism rings.Graduations measured in degrees are marked on the base. The lensblocking device contains means for supporting a lens blank to be blockedand for aligning the cylindrical and optical axes of a premarked lensblank with the device. Means are de scribed for introducing a lowmelting point blocking metal into a mold cavity defined by the prismrings, the base and the lens blank. Means for cooling the blocking metaland for the easy removal of the solidifed block with attached lens blankare also described. Means are described for holding the prism rings incoaxial and rotatable contact with each other and with the base.

7 Claims, 8 Drawing Figures FATENTED FEB 1 8 5975 SHEET 3 BF 4 LENSBLOCKING DEVICE BACKGROUND OF THE INVENTION This application relates tothe blocking of lens blanks and more particularly relates to an improvedapparatus for the blocking of lens blanks so that in subsequentgenerating operations a desired prism can be ground into the lens.

In the manufacture of ophthalmic lenses, a lens blank is formed into afinished lens by successively grinding and then polishing first onesurface and then the other. Usually one surface is concave and the otherconvex, and the two surfaces have different curvatures, so that thethickness of the lens varies at different points. This variation inthickness gives the optical refraction necessary to provide the desiredcorrection in vision.

A lens blank having one of its two surfaces ground and polished istermed a semi-finished lens. The subsequent generation of the oppositesurface is a more exacting operation because the second surface must notonly have the correct curvature, but must bear an exact and preciserelation to the previously finished surface, in order for the lens tohave the ophthalmic properties desired. This precise location of thesecond surface with respect to the first may require either or both oftwo adjustments or settings, one called prism" and the other calledaxis." Setting for prism involves a tilting of the second surface withrespect to the first, and setting for axis involves a rotation of thesecond surface with respect to the first.

The problem of correctly relating the second surface to the first hasheretofore been met by mounting a lens blank on a lens block in aconventional manner and then adjusting the block in the chuck of agenerating machine so that the desired amount of prism at the correctmeridian could be ground into the lens. One device for incorporatingprism into the lens in this manner is disclosed in US. Pat. No. to Allenet al. 2,879,632.

Another technique that has been used is that in which the desired amountof prism at the prescribed meridian is incorporated directly into thelens block so that when the block is mounted in a conventional manner ina grinding machine the desired prism is ground into the lens. Prior artdevices of this type are exemplified by US. Pat. Nos. to Buckminster3,049,766 and Prunier 3,195,197. These latter devices use a blockingsystem in which molten metal of low melting point, while constrained ina mold, is cast directly on the lens surface. The desired amount ofprism is incorporated into the block by either tilting the lens withpins as the lens is presented to the mold, or by selecting and insertinginto the device one of several support rings which provide the desiredamount of tilt to the lens as it is presented to the mold. These devicesare complicated and expensive to construct and maintain. In addition, inthe tilting pin device molten metal may infiltrate into the pin sleeveareas and interfere with the blocking operation. In the selected supportring device, in order to incorporate the desired amount of prism intothe block, a large inventory of support rings is required and theconstant handling thereof results in undesirable wear and replacementproblems.

SUMMARY OF THE INVENTION It is an object of the present invention toprovide a block of the low melting point metal type which is preciselyaccurate, simple to operate, free of substantially all maintenanceproblems and requires no substitution of parts.

The present invention is for a device for blocking lens blanks which areultimately to be provided with a prescriptive prism correction, i.e.,where one side of the lens blank is to be finished thicker than itsdiametrically opposed side along a predetermined axis through theoptical center of the lens blank.

When blocking a lens that is to be finished with a cylinder andprismatic correction it is important that the amount of prism, measuredin diopters, be accurately introduced into the lens. It is equallyimportant that the prism axis be oriented in the prescribed meridian andin proper relation to the cylinder axis of the lens.

In the present invention a low melting point blocking metal isintroduced into a water-cooled, generally cylindrically-shaped moldcavity. The upper portion of the mold incorporates a lens support ring,and a lens blank is positioned on the lens support ring and serves asthe upper closure of the mold. The blocking metal is such that when thecavity is filled, and as the metal hardens, it becomes attached to thelens blank. The hardened metal also forms the block for the blank. Thelens support ring may be adjusted relative to the axis of the mold toposition the lens blank in a manner such that when the blocking metal isintroduced into the mold, the prescribed amount of prism may beincorporated into the block at the desired meridianal orientation. Thecast block is also provided with aligned recesses which serve properlyto position the block, with the attached lens blank, in the chuck of thesurfacing machines subsequently used to grind and polish the lens to thedesired finish.

The semi-finished lens blank which serves as the upper closure for themold is first marked on the finished surface in a conventional markingdevice to designate the optical center and cylindrical axis of the lens.The support ring, which is integral with the upper one of a pair ofwedge-shaped prism rings mounted on the blocking device, is then rotatedwith respect to its mating wedgeshaped prism ring to align graduationson the two rings and provide the required amount of diopter prism. Thetwo aligned prism rings are then rotated together with respect to theblocking device until the prism axis is located in the requiredmeridian. The premarked lens blank is then placed on the lens block moldcavity with its finished side against the support ring. The blank isadjusted manually on the support ring until the marks on the blank arealigned with reference indicia incorporated in the blocking device.Metal blocking alloy is then introduced into the cavity beneath the lensand solidified. The resulting lens block assembly with the desired axisand degree of diopter prism accurately incorporated therein is readilyremoved from the blocking device for subsequent finishing of the lens.

There is a minimum number of moving parts to the device. Molten blockingmetal cannot penetrate into the prism adjusting mechanism. The blockingdevice may be used to introduce prism of any amount and at any axis intothe block for any lens without requiring a change or substitution ofparts in the device. Adjustments for the degree and axis of prism aremade using direct readings from graduations provided on the device.Either concave or convex lens surfaces may be presented to the devicefor blocking.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of a blockingdevice showing a lens blank in dash line positioned on the device.

FIG. 2 is a vertical section, taken generally along the line 2-2 of FIG.1, and showing a lens blank being blocked to incorporate a predeterminedamount of prism at a predetermined axis.

FIG. 3 is a view similar to FIG. I, but showing a different setting forprism and axis.

FIG. 4 is a front elevational view, partly in vertical section, takenalong the line 44 of FIG. 3.

FIG. 5 is an exploded perspective view of the adjustable wedge-shapedprism rings of my invention together with a C-shaped retaining ring.

FIG. 6 is a perspective view of a lens blocked in accordance with myinvention.

FIG. 7 is an exploded perspective view of the wedgeshaped prism ringsshowing a modified means for maintaining the rings in contact with oneanother.

FIG. 8 is a front elevation, partly in vertical section, of a blockingdevice embodying the modification shown in FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION Referring now to the drawings, abase, generally designated 10, having cooling passages 12 connected tocooling water inlet-outlet 14 has a central, cylindrically shaped bore16. A piston 18 is slidably mounted for axial reciprocation within bore16. Coil springs 20 are interposed between the head 22 of piston 18 andthe top of hollow mandrel 24. Springs 20 serve constantly to urge piston18 to its uppermost position within bore 16. Springs 20 are held inplace by bosses 26.

The head 22 of piston 18 has three diametrically aligned cylindricalpassages 28, 30, 32, in each of which is disposed a light transmittingmedium 34, such as a bundle of fiber optics. Mounted on head 22 is apair of generally comically-shaped protrusions 36, 38. These protrusions36, 38 are in diametral alignment and are coaxial with passages 28 and32, respectively. Intermediate protrusions 36, 38 and diametrallyaligned therewith is centrally located hollow protrusion 40 having alower frusto-conical wall section 41 and an upper frusto-conical wallsection 42 connecting wall section 41 with cylindrical section 44.Section 44 has a small bore (FIG. 1) axially aligned in the centerthereof. Bore 50 is axially aligned with passage 30. Within each of theprotrusions 36, 38 is a small bore 46, 48, respectively, axially alignedwith passages 28 and 32, respectively.

A source of illumination such as light bulb 52 is mounted atop mandrel24 and is connected to a conventional current source, not shown. Lightemitted from bulb 52 passes through light transmitting medium 34 and isvisible through bores 46, 48 and 50 when viewed directly from above.

The head 22 of spring mounted piston 18 also contains protrudingsegments 54 through one of which extends a cylindrical conduit 56(FIG. 1) which serves as an inlet for molten metal.

Base also contains horizontally disposed slots 58, 60 terminating inupwardly extending apertures 62, 64, respectively. A J-shaped clampingmember 66 is disposed within each of the slots 58, 60. A ball plunger 68is disposed within base 10 beneath each clamping member 66. The ball onthe head of plunger 68 seats in an aperture in clamping member 66.

A wedge-shaped lower prism ring, generally designated 70, having acounterbored portion 72 seats on the upper annular surface 74 of base10. An annular groove 76 is cut into the wall 78 of counterbored portion72. Groove 76 is adapted to receive the inner end of .I-shaped clampingmembers 66. When the inner end of J-shaped clamping member 66 is seatedin groove 76, the lower prism ring is held in axial alignment with andis in rotatable contact with base 10.

Lower prism ring 70 is coaxial with the reciprocable piston 18. The flatannular bottom surface 94 and the flat annular surface of counterboredportion 72 of lower prism ring 70 are normal to the axis of prism ring70. Upper generally annular surface 80 of lower prism ring 70 isinclined with respect to the bottom surface 94 of the lower prism ring,thus giving the ring a wedge shape.

The upper surface 80 of lower prism ring 70 has an upwardly extending,centrally located annular flange portion 82. The lower prism ring has agenerally cylindrical central bore 84, the wall of which is inclinedoutwardly with respect to the axis of the lower prism ring in the upwarddirection for purposes to be explained more fully hereinafter. As shownin FIGS. 2 and 5, the wall of bore 84 is stepped to present a shoulder86 within the bore.

The upper annular flange portion 82 of lower prism ring 70 has a flatupper annular surface 90. Surface 90 is parallel to surface 80 and bothsurfaces are inclined with respect to the axis of lower prism ring 70.Surface 90 serves as a seat for upper prism ring, generally designated102, as described hereinafter. For approximately 270 of itscircumferential outer edge, upper flat surface 80 connects withcylindrical wall 92. Wall 92 extends downwardly and connects directlywith the bottom annular flat surface 94 of lower prism ring 70. For theremaining segment of about 1 10 of its circumference, flat surface 80 isseparated from wall 92 by sloping surface 96. A 90 segment of thesurface 96 has prism scale graduations 124 marked thereon. That portionof flat surface 80 that is angularly coextensive with sloping surface 96has corresponding prism scale graduations 126 marked thereon forpurposes to be described more fully hereinafter. Lower prism ring 70 hasthreaded apertures 98 adapted to receive screws 100 (FIG. 1).

Axially aligned with lower prism ring 70 is wedgeshaped upper prismring, generally designated 102, having a flat annular bottom surface 103and a counterbored portion 104. Flat annular surface 106 of thecounterbored portion of ring 102 is parallel to surface 103 and seats onthe flat annular surface 90 of lower ring 70. The wall of counterboredportion 104 of the upper ring is slightly larger in diameter than theouter wall of annular flange 82 of the lower ring and forms a slidingfit therewith. Upper ring 102 is rotatable with respect to lower ring 70about the axis of ring 70. Contact between the wall of counterboredportion 104 and the outer wall of flange 82 holds rings 70 and 102 inaxial alignment with one another. Flat annular surface 106 of ring 102is contiguous with flat annular surface 90 of ring 70. These faces areinclined with respect to the axis of lower prism ring 70.

Upper ring 102 has a centrally located bore 108. The wall of bore 100 isinclined outwardly with respect to the axis of the ring in the upwarddirection. The upper annular surface 110 of ring 102 is inclined withrespect to the bottom surface 103. The inner edge of upper surface 110connects with upwardly extending annular flange portion 112 having athin annular upper edge 118 which serves as a support ring for a lensblank 122. Prism scale graduations 120 extend through a segment of 90 ofthe surface 110 of the upper prism ring, as will be more fully describedhereinafter.

Coaxial with the upper and lower prism rings is C- shaped retaining ring114. As shown in FIGS. 1 and 5, ring 114 extends in an arc of about 270,and is of the same diameter as lower prism ring 70. The inner diameterof ring 1 14 is less than the outer diameter of upper prism ring 102.l-loles 116, adapted to receive screws 100, are drilled in ring 114.

The exploded view of FIG. 5 shows the relative positions of the C-shapedretaining ring 114, upper prism ring 102 and lower prism ring 70. Asshown in FIG. 2, when assembled, screws 100 pass through holes 116 andinto threaded apertures 98 of the lower ring, thus securing ring 114 tolower prism ring 70. Ring 102 is held between rings 114 and 70 and isrotatable with respect-to rings 114 and 70 about an axis common to allthree rings.

As shown in FIG. 2, base and piston 18 form the bottom wall of moldcavity 120, and the upper and lower prism rings 102 and 70,respectively, form the side wall of the cavity. Lens blank 122,supported on the upper edge 118 of upper prism ring 102, forms the topof the mold cavity.

Referring again to FIG. 1, base 10 has a flat upper surface 00. Axisscale graduations 132 extend completely around base 10 on circle havinga diameter that is equal to the outer diameter of lower prism 70. Theaxis scale graduations are in degrees and run from 0 through 180 in theupper, clockwise direction, as well as from 0 through 180 in the lower,counterclockwise direction. The 0 and 180 markings are on a diameter 130that is coincident with the diametrally aligned protrusions on piston10. 1 refer to diameter 130 as the base apex line. The lower,counterclockwise axis scale graduations 132 are used when a convex lensblank surface is presented to the blocking device as shown in FIG. 2.The upper, clockwise axis scale graduations are used when a concave lensblank surface is presented to the blocking device.

The prism scales 120 on upper prism ring 102 are calibrated in prismdiopters. The calibrations run from 5 to 0. The 5 mark is placed at thethinnest point on the ring. A plane in contact with the upper edge 118of ring 102 for the full circumference thereof forms an angle of 2 44'with the plane of the bottom 103 of the ring 102.

Prism scales 124 and 126 on lower prism ring 70 are also calibrated inprism diopters, the calibrations running from 5 to 0. The 5 mark on thelower prism ring is also at the thinnest point on the ring. A plane incontact with the flat annular surface 90 of lower prism ring '70 for thefull circumference thereof forms an angle of 2 44' with the plane ofbottom surface 94 of the ring 70.

The prism scale markings on both the upper and lower prism rings aregraduated from 5 to 0 with 5 at the thinnest point on each of the rings,through an angle of 90, as follows:

It will be apparent from an examination of FIG. 1 that not all of themarkings of the prism scales 124, 126 and 128 are shown on the drawing,the number of graduations shown being reduced for clarity. Similarly,not all of the degree markings of the axis scale 132 are shown; again,the number illustrated being reduced for clarity.

In order to introduce the prcper amount of prism at the correct prismorientation into a lens to be blocked on the lens blocking device of theinvention, the upper prism ring 102 is first rotated with. respect tothe lower prism ring to register the desired prism scale graduation 128on the upper ring 102 with the appropriate prism scale graduation 126 onthe lower ring 70. The upper and lower rings are then rotated as a unitto the appropriate axis scale graduation 132 to orient the prism anglein the proper meridian.

As stated above, prism scales 124 and 126 are marked on lower prism ring70. The angular placement of the graduations is the same for each scale124 and 126. Scale 126 is used to align the graduations on the upperprism ring 102 with the graduations on the lower prism ring 70. Scale124 is then used to align the amount of prism with the graduations onthe axis scale 132.

As a specific example, and as shown in FIGS. 1 and 2, if a lens is to beblocked to generate a minus curve of 3.5 diopters of prism at an angleof 43, the amount of prism is obtained by aligning the 3.5 marking onscale 128 with the 3.5 marking on scale 126. The aligned prism rings arethen rotated as a unit relative to the base to a point where the 3.5marking on scale 124 is aligned with the 43 graduation on the axis scale132. This 43 point will be the apex of the prism that will beincorporated into the lens in subsequent blocking and generatingoperations.

Another example is illustrated in FIGS. 3 and 4. There the lens is to beblocked to generate a minus curve of 5 diopters of prism at an angle of10. The marking 5 on scale 128 of upper prism ring 102 is aligned withthe marking 5 on scale 126 of lower prism ring 70. The upper and lowerrings 102 and 70, respectively, are then rotated as a unit relative tobase 10 until the 5 marking on scale 124 is aligned with the 10graduation on the axis scale 132. This 10 point will be the apex of theprism that will be incorporated into the lens.

Once the proper amount and orientation of the prism has been establishedby rotating the prism rings as described, a lens blank 122 previouslygiven a thin coating of material that will assure good adhesion theretoof the metal blocking alloy and marked in a manner well known to thoseskilled in the art to designate the cylinder axis (indicated by the dashline 133 in FIG. 1), as well as the optical axis of the lens (indicatedby the intersection of short vertical line 134 and line 133), is broughtinto contact with protrusion 40 extending upwardly from the head 22 ofspring mounted reciprocatable piston 18. The lens blank is then urgeddownwardly against the resistance of coil springs 20, until the lensblank seats on the upper edge 118 (lens support ring) of upper prismring 102. The previously marked cylinder axis of the lens is thenaligned with the diametrically aligned bores 46, 48 of the protrusions36, 38, respectively, and the optical axis of the lens is aligned withbore 50. This alignment is facilitated by observing light emitted bylight bulb 52 and transmitted upwardly through passages 28, 30 and 32 ofthe head 22 by the bundles of light transmitting fiber optics 34disposed therein. This light will, of course, pass through the lens 122and is visible when viewed from above the lens. It will be noted thatwhen aligned, the cylindrical axis 133 of the lens is also aligned withthe base axis line 130.

After the axis and optical center of the lens are properly positioned, aholding member 136 having a pressure pad 138 of resilient material atthe lower end thereof secures the lens blank to the blocking device. Thefinished surface of the lens blank now forms the upper wall of moldcavity 120. Molten metal blocking alloy is then injected through conduit56 into the mold cavity 120 beneath the lens. Cooling liquid 140circulating through base causes the blocking metal to solidify,resulting in a lens-block assembly with the desired amount of prism andprism axis incorporated in the assembly.

Upon solidification of the blocking metal, reciprocatable head 18 iswithdrawn downwardly into the base a short distance by means, not shown,and then returned under the force of slightly compressed coil springsagainst the solidified block. This causes the solidified block andattached lens blank to be jarred loose from the blocking device. Theremoval of the block and attached lens blank is facilitated by theoutward inclination of bore 84 of the lower prism ring 70 and theoutward inclination of bore 108 of upper prism ring 102, as describedabove. Shoulder 86 within bore 84 of the lower prism ring preventsjamming of the solidified block against the outer wall of bore 84 onwithdrawal of the head 18 as described.

The completed lens-block assembly when removed from the blocking deviceis shown in FIG. 6 with the lens blank' 122 attached to the block,generally designated 142. The shank 144 of block 142 is of uniformdimension in the axial direction. The head 146 of the block is thicker,i.e., has a greater dimension in the axial direction, on one sidethereof than on its diametrally opposed side. This difference inthickness represents the amount of prism that is incorporated in thelens-block assembly. It will be understood, of course, that the upperand lower prism rings may be adjusted so that no prism is introducedinto the block. This, for

example, will be the case where the O graduation on the prism scale 128is aligned with the 0 graduation on the prism scale 126.

The tang portion 148 of block 142 has diametrally alignedconically-shaped recesses 150 and 152 corresponding to protrusions 36and 38 on piston 18. Center recess 154 having center opening 156 thatextends completely through the block, and corresponding to protrusion 40on piston 18, is diametrally aligned with recesses 150 and 152. Thethree recesses function as axis aligning means when the block ispresented to the chuck of a lens grinding machine for subsequentgeneration of the desired surface on the unfinished surface of the lensblank. Sprue 158, through which the molten blocking metal flowed intomold cavity 120 through conduit 56, is shown adjacent the tang of theblock.

A modification of the means for maintaining the upper and lower prismrings in axial alignment, and without the necessity of retaining ring 114, is shown in FIGS. 7 and 8. A plurality of cylindrically shapedpermanent magnets 160 are shrunk fit into correspondingly shapedopenings 162 drilled into the slightly raised, upper flat annularsurface 164 of wedge-shaped lower prism ring 166. The bottom surface 168of wedge-shaped upper prism ring 170 is countersunk to form an annularrecess having a corresponding flat annular surface 172 that seatsagainst surface 164 and is rotatably held in place thereon by magnets160. Shoulder 174 which has a sliding fit in the annular recess ofbottom surface 168 maintains the two rings in axial alignment. The twocontiguous flat surfaces 164 and 172 are inclined with respect to theaxis of lower prism ring 166. Lower ring 166is held in axial alignmentand in rotatable contact with base 10 by J-shaped clamping members 66 inthe same manner as described in connection with the embodiments shown inFIGS. 1 through 5.

Operation of the modified embodiment illustrated in FIGS. 7 and 8 isidentical with that described in connection with the embodiment shown inFIGS. 1 through 6. It will be understood that while the strength ofmagnets 160 is great enough to maintain the upper and lower prism rings170 and 166, respectively, in rotatable engagement with one another, themagnets are not so strong as to interfere with the rotation of the tworings with respect to each other to align the graduations on the prismscales as desired, nor do the magnets interfere with the rotation of thealigned prism rings with respect to base 10 in order to orient the prismto the desired meridian.

The terms and expressions which have been employed here are used asterms of description and not of limitation, and there is no intention,in the use of such terms and expressions, of excluding equivalents ofthe features shown and described, or portions thereof, it beingrecognized that various modifications are possible within the scope ofthe invention claimed.

I claim:

1. A lens blocking device comprising a pair of wedge-shaped prism rings,one of which is rotatably adjustable relative to the other about theaxis of said one of said rings,

said rings having contiguous plane faces which are inclined with respectto the axis of said one of said rings,

means for holding said rings in axial alignment and in rotatable contactwith one another,

indicia on each of said rings for selecting a predetermined amount ofprism in diopters by rotating said rings relative to each other,

a base,

means for holding said one of said rings in axial alignment and inrotatable contact with said base,

indicia on said base for selecting a predetermined prism axis byrotating said rings relative to said base,

means on the distal face of the other of said rings for engaging thesurface of a lens blank to be blocked, said rings, base and lens blanksurface defining a cavity shaped to form a lens block,

and means for supplying molten metal to said cavity for molding saidlens block in said cavity and adhering it to said lens blank, whereby apredetermined amount of prism in diopters and a predetermined meridianalorientation of said prism may be incorporated into siad lens block.

2. A lens blocking device as defined in claim 1 wherein said lens blankis provided with indicia designating the optical axis and cylinder axisthereof and said base comprises means for aligning said lens blank withrespect to said base.

3. A lens blocking device as defined in claim 1 wherein said basefurther comprises means for removing said block from said cavityincluding a piston reciprocable in the direction of the axis of said oneof said rings.

4. A lens blocking device as defined in claim 1 wherein said means forholding said rings in axial alignment and in rotatable contact with oneanother comprise a C-shaped retaining ring and means for fixedlyattaching said retaining ring to said one of said pair of rings with theother of said pair of rings being rotatably disposed axially betweensaid retaining rings and said one of said pair of rings.

5. A lens blocking device as defined in claim 1 wherein said means forholding said rings in axial alignment and in rotatable contact with oneanother comprise a plurality of permanent magnets disposed in said oneof said rings, said other of said rings being of material attracted bysaid magnets.

6. A lens blocking device as defined in claim 1 wherein said means forholding the distal face of said one of said pair of rings in rotatablecontact with said base comprise a J-shaped clamping member in said base,the inner end of said member being adapted to be received in an annulargroove in said one of said pair of rings.

7. A lens blocking device as defined in claim 1 fur ther comprisingmeans for holding said lens blank in contact with said lens engagingmeans.

UNITED STATES PATENT OFFICE QERTIFICATE 0F CORRECTION PATENT NO.3,866,667

DATED Feb. 18, 1975 tNvENTORtS) I Lloyd F. Knight it is certified thaterror appears in the aboverdentrfied patent and that said Letters Patentare hereby corrected as shown below:

In abstract, lines 15-16, change "solidifec't" to --solidified.

Col. 3, line 49, insert "50" after -bore-.

In clalnh 4, line 9, change "rings" to -ring-.

Signed and Sealed this eleventh Day of May 1976 [SEAL] A nest:

RUTH C. MASON Arroxrmg ()ffr'eer C. MARSHALL DANN Commissioner of Pan-msand Trademarks

1. A lens blocking device comprising a pair of wedge-shaped prism rings,one of which is rotatably adjustable relative to the other about theaxis of said one of said rings, said rings having contiguous plane faceswhich are inclined with respect to the axis of said one of said rings,means for holding said rings in axial alignment and in rotatable contactwith one another, indicia on each of said rings for selecting apredetermined amount of prism in diopters by rotating said ringsrelative to each other, a base, means for holding said one of said ringsin axial alignment and in rotatable contact with said base, indicia onsaid base for selecting a predetermined prism axis by rotating saidrings relative to said base, means on the distal face of the other ofsaid rings for engaging the surface of a lens blank to be blocked, saidrings, base and lens blank surface defining a cavity shaped to form alens block, and means for supplying molten metal to said cavity formolding said lens block in said cavity and adhering it to said lensblank, whereby a predetermined amount of prism in diopters and apredetermined meridianal orientation of said prism may be incorporatedinto siad lens block.
 2. A lens blocking device as defined in claim 1wherein said lens blank is provided with indicia designating the opticalaxis and cylinder axis thereof and said base comprises means foraligning said lens blank with respect to said base.
 3. A lens blockingdevice as defined in claim 1 wherein said base further comprises meansfor removing said block from said cavity including a piston reciprocablein the direction of the axis of said one of said rings.
 4. A lensblocking device as defined in claim 1 wherein said means for holdingsaid rings in axial alignment and in rotatable contact with one anothercomprise a C-shaped retaining ring and means for fixedly attaching saidretaining ring to said one of said pair of rings with the other of saidpair of rings being rotatably disposed axially between said retainingrings and said one of said pair of rings.
 5. A lens blocking device asdefined in claim 1 wherein said means for holding said rings in axialalignment and in rotatable contact with one another comprise a pluralityof permanent magnets disposed in said one of said rings, said other ofsaid rings being of material attracted by said magnets.
 6. A lensblocking device as defined in claim 1 wherein said means for holding thedistal face of said one of said pair of rings in rotatable contact withsaid base comprise a J-shaped clamping member in said base, the innerend of said member being adapted to be received in an annular groove insaid one of said pair of rings.
 7. A lens blocking device as defined inclaim 1 further comprising means for holding said lens blank in contactwith said lens engaging means.